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| United States Patent |
6,057,633
|
|
Inoi
, et al.
|
May 2, 2000
|
Piezoelectric transformer unit
Abstract
In order to achieve the above and other objects, a piezoelectric
transformer unit is provided. The unit contains a piezoelectric
transformer element, a first upper electrode, a first lower electrode, an
insulator casing, a first lead terminal, and an insulator elastic member.
The piezoelectric transformer element has a upper element surface, a lower
element surface, and a first side element surface. The first upper
electrode is formed on the upper element surface of the piezoelectric
transformer element, and the first lower electrode is formed on the lower
element surface of the piezoelectric transformer element. The insulator
casing houses the piezoelectric transformer element. The first lead
terminal protrudes from an inner surface of the insulator casing, supports
the piezoelectric transformer element within the insulator casing, and
vertically presses the an oscillation nodal point of the piezoelectric
transformer element. The insulator elastic member is arranged between an
oscillation nodal point on one of the upper, lower, and first side element
surfaces of the piezoelectric transformer element and the insulator
casing.
| Inventors:
|
Inoi; Takayuki (Tokyo, JP);
Taihaku; Naoto (Tokyo, JP);
Suzuki; Hiromi (Tokyo, JP)
|
| Assignee:
|
NEC Corporation (Tokyo, JP)
|
| Appl. No.:
|
098437 |
| Filed:
|
June 17, 1998 |
Foreign Application Priority Data
| Current U.S. Class: |
310/345; 310/348 |
| Intern'l Class: |
H01L 041/08 |
| Field of Search: |
310/344,346,348,354-356,358,359
|
References Cited
U.S. Patent Documents
| 4034318 | Jul., 1977 | Ishiyama et al. | 310/345.
|
| 4511821 | Apr., 1985 | Nakamura et al. | 310/344.
|
| 5250870 | Oct., 1993 | Fenlon et al. | 310/345.
|
| 5365141 | Nov., 1994 | Kawai et al. | 310/359.
|
| 5440195 | Aug., 1995 | Ohnishi et al. | 310/359.
|
| 5747916 | May., 1998 | Sugimoto et al. | 310/348.
|
| 5841217 | Nov., 1998 | Kizaki et al. | 310/345.
|
| 5859488 | Jan., 1999 | Okeshi et al. | 310/348.
|
| 5880553 | Mar., 1999 | Okeshi et al. | 310/344.
|
| Foreign Patent Documents |
| 0148361 | Jul., 1985 | EP.
| |
| 0730312 | Sep., 1996 | EP.
| |
| 06342945 | Dec., 1994 | JP | 310/345.
|
| 8-298213 | Nov., 1996 | JP.
| |
Other References
M. Sugimoto et al., "Very Compact Inverter for Color LCD Backlight
Utilizing a Packaged Piezolectric Ceramic Transformer", SID 96 Digest,
1996, pp. 757-760 No Month.
Kawashima et al., "Development of Color-LCD Backlight Inverters Utilizing
Piezoelectric Transformer", NEC Res. & Develop., vol. 36, No. 1, Jan.
1995, pp. 187-192.
|
Primary Examiner: Budd; Mark O.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas, PLLC
Claims
What is claimed:
1. A piezoelectric transformer unit, comprising:
a piezoelectric transformer element having a upper element surface, a lower
element surface, and a first side element surface;
a first upper electrode formed on said upper element surface of said
piezoelectric transformer element;
a first lower electrode formed on said lower element surface of said
piezoelectric transformer element;
an insulator casing which houses said piezoelectric transformer element;
a first lead terminal which protrudes from an inner surface of said
insulator casing, supports said piezoelectric transformer element within
said insulator casing, and vertically presses an oscillation nodal point
of said piezoelectric transformer element; and
first, second, third, and fourth elastic adhesives, wherein said first to
fourth elastic adhesives are respectively located at first to fourth
oscillation nodal points of said piezoelectric transformer element,
wherein said first elastic adhesive is disposed next to an upper casing
surface and a first side casing surface of said insulator casing and is
disposed next to said upper element surface and said first side element
surface of said piezoelectric transformer element,
wherein said second elastic adhesive is disposed next to said upper casing
surface and said first side casing surface and is disposed next to said
upper element surface and said first side element surface,
wherein said third elastic adhesive is disposed next to a lower casing
surface and a second side casing surface of said insulator casing and is
disposed next to said lower element surface and a second side element
surface of said piezoelectric transformer element, and
wherein said fourth elastic adhesive is disposed next to said lower casing
surface and said second side casing surface and is disposed next to said
lower element surface and said second side element surface.
2. The piezoelectric transformer unit as claimed in claim 1, wherein said
first elastic adhesive is substantially disposed at a mid point of a
dimension of said first upper electrode, wherein said dimension of said
first upper electrode is parallel to said first side element surface, and
wherein said third elastic adhesive is substantially disposed at a mid
point of a dimension of said first lower electrode, wherein said dimension
of said first lower electrode is parallel to said second side element
surface.
3. The piezoelectric transformer unit as claimed in claim 2, wherein said
piezoelectric transformer element has a second upper electrode disposed on
said upper element surface and a second lower electrode disposed on said
lower element surface,
wherein said second elastic adhesive is substantially disposed at a mid
point of a dimension of said second upper electrode, wherein said
dimension of said second upper electrode is parallel to said first side
element surface, and
wherein said fourth elastic adhesive is substantially disposed at a mid
point of a dimension of said second lower electrode, wherein said
dimension of said second lower electrode is parallel to said second side
element surface.
4. The piezoelectric transformer unit as claimed in claim 3, wherein said
piezoelectric transformer element has a third upper electrode disposed
between said first upper electrode and said second upper electrode and has
a third lower electrode disposed between said first lower electrode and
said second lower electrode, and
wherein a fifth elastic adhesive is disposed between said first and second
elastic adhesives and is disposed next to said lower casing surface and
said first side casing surface and is disposed next to said lower element
surface and said first side element surface.
5. The piezoelectric transformer unit as claimed in claim 4, wherein
respective ends of said third upper electrode and said third lower
electrode are connected via a side electrode on one of said first and
second side element surfaces, and
wherein said first lead terminal is a first lower lead terminal which
contacts said first lower electrode,
wherein a first upper lead terminal is disposed above said first lower lead
terminal and contacts said first upper electrode,
wherein a second upper lead terminal contacts said third upper electrode,
and
wherein no lead terminal contacts said third lower electrode.
6. A piezoelectric transformer unit, comprising:
a piezoelectric transformer element having a upper element surface, a lower
element surface, and a first side element surface;
a first upper electrode formed on said upper element surface of said
piezoelectric transformer element;
a first lower electrode formed on said lower element surface of said
piezoelectric transformer element;
an insulator casing which houses said piezoelectric transformer element;
a first lead terminal which protrudes from an inner surface of said
insulator casing, supports said piezoelectric transformer element within
said insulator casing, and vertically presses an oscillation nodal point
of said piezoelectric transformer element; and
an insulator elastic member arranged between an oscillation nodal point on
one of said upper, lower, and first side element surfaces of said
piezoelectric transformer element and said insulator casing,
wherein said insulator elastic member comprises:
a first elastic projection projecting from said one of said upper, lower,
and first side element surfaces of said piezoelectric transformer element.
7. The piezoelectric transformer unit as claimed in claim 6, further
comprising:
a second elastic projection,
wherein said first and second elastic projections are respectively located
at first and second oscillation nodal points of said piezoelectric
transformer element.
8. The piezoelectric transformer unit as claimed in claim 7, wherein said
first elastic projection is a first side elastic projection and is
disposed next to a first side casing surface of said insulator casing and
projects from said first side element surface of said piezoelectric
transformer element, and
wherein said second elastic projection is a second side elastic projection
and is disposed next to a second side casing surface of said insulator
casing and projects from a second side element surface of said
piezoelectric transformer element.
9. The piezoelectric transformer unit as claimed in claim 8, further
comprising:
third and fourth side elastic projections,
wherein said fourth side elastic projections are respectively located at
third and fourth oscillation nodal points of said piezoelectric
transformer element,
wherein said third side elastic projection is disposed next to said first
side casing surface and projects from said first side element surface, and
wherein said fourth side elastic adhesive is disposed next to said second
side casing surface and projects from said second side element surface.
10. The piezoelectric transformer unit as claimed in claim 9, further
comprising:
fifth and sixth side elastic projections,
wherein said fifth and sixth side elastic projections are respectively
located at fifth and sixth oscillation nodal points of said piezoelectric
transformer element,
wherein said fifth side elastic projection is disposed next to a third side
casing surface of said insulator casing and projects from a third side
element surface of said piezoelectric transformer element, and
wherein said sixth side elastic projection is disposed next to a fourth
side casing surface of said insulator casing and projects from a fourth
side element surface of said piezoelectric transformer element.
11. The piezoelectric transformer unit as claimed in claim 10, wherein said
first side element surface opposes said second side element surface and
wherein said third side element surface opposes said fourth side element
surface.
12. The piezoelectric transformer unit as claimed in claim 10, wherein said
first side elastic projection is substantially disposed at a first mid
point of a first dimension of said first upper electrode, wherein said
first dimension of said first upper electrode is parallel to said first
side element surface, and
wherein said second side elastic projection is substantially disposed at a
second mid point of a second dimension of said first upper electrode,
wherein said second dimension of said first upper electrode is parallel to
said second side element surface.
13. The piezoelectric transformer unit as claimed in claim 12, wherein said
piezoelectric transformer element has a second upper electrode disposed on
said upper element surface and a second lower electrode disposed on said
lower element surface,
wherein said third side elastic projection is substantially disposed at a
first mid point of a first dimension of said second upper electrode,
wherein said first dimension of said second upper electrode is parallel to
said first side element surface, and
wherein said fourth side elastic projection is substantially disposed at
second a mid point of a second dimension of said second upper electrode,
wherein said second dimension of said second upper electrode is parallel
to said second side element surface.
14. The piezoelectric transformer unit as claimed in claim 13, wherein said
fifth side elastic projection is substantially disposed at a third mid
point of a third dimension of said first upper electrode, wherein said
third dimension of said first upper electrode is parallel to said third
side element surface, and
wherein said sixth side elastic projection is substantially disposed at
third a mid point of a third dimension of said second upper electrode,
wherein said third dimension of said second upper electrode is parallel to
said fourth side element surface.
15. The piezoelectric transformer unit as claimed in claim 14, further
comprising:
a first upper elastic projection projecting from said upper surface of said
piezoelectric transformer element and disposed next to an upper casing
surface of said insulator; and
a first lower elastic projection projecting from said lower surface of said
piezoelectric transformer element and disposed next to a lower casing
surface of said insulator.
16. The piezoelectric transformer unit as claimed in claim 15, further
comprising:
a second upper elastic projection projecting from said upper surface of
said piezoelectric transformer element and disposed next to said upper
casing surface of said insulator; and
a third lower elastic projection projecting from said lower surface of said
piezoelectric transformer element and disposed next to a lower casing
surface of said insulator.
17. The piezoelectric transformer unit as claimed in claim 16, wherein said
first upper elastic projection is located between said first upper
electrode and said first side element surface, and
wherein said second upper elastic projection is located between said second
upper electrode and said first side element surface.
18. The piezoelectric transformer unit as claimed in claim 17, wherein said
first lower elastic projection is located between said first lower
electrode and said second side element surface, and
wherein said second lower elastic projection is located between said second
lower electrode and said second side element surface.
19. The piezoelectric transformer unit as claimed in claim 18, wherein said
first upper elastic projection is substantially directly located above
said first side elastic projection,
wherein said second upper elastic projection is substantially directly
located above said third side elastic projection,
wherein said first lower elastic projection is substantially directly
located below said second side elastic projection, and
wherein said second lower elastic projection is substantially directly
located below said fourth side elastic projection.
20. The piezoelectric transformer unit as claimed in claim 19, wherein a
third upper electrode is provided on said upper element surface between
said first and second upper electrodes, and
wherein a third lower electrode is provided on said lower element surface
between said first and second lower electrodes,
wherein a third upper elastic projection projects from said upper element
surface and is located adjacent to a side of said third upper electrode,
and
wherein a third lower elastic projection projects from said lower element
surface and is located adjacent to a side of said third lower electrode.
21. The piezoelectric transformer unit as claimed in claim 20, wherein said
third upper elastic projection is disposed next to said second side
element surface and said third lower elastic projection is disposed next
to said first side element surface.
22. The piezoelectric transformer unit as claimed in claim 14, wherein said
insulator elastic member comprises:
first and second upper elastic adhesives applied to an upper casing surface
of said insulator casing; and
first and second lower elastic adhesives applied to a lower casing surface
of said insulator casing.
23. The piezoelectric transformer unit as claimed in claim 22, wherein said
first upper elastic adhesive is located between said first upper electrode
and said first side element surface, and
wherein said second upper elastic adhesive is located between said second
upper electrode and said first side element surface.
24. The piezoelectric transformer unit as claimed in claim 23, wherein said
first lower elastic adhesive projection is located between said first
lower electrode and said second side element surface, and
wherein said second lower elastic adhesive is located between said second
lower electrode and said second side element surface.
25. The piezoelectric transformer unit as claimed in claim 24, wherein said
first upper elastic adhesive is substantially directly located above said
first side elastic projection,
wherein said second upper elastic adhesive is substantially directly
located above said third side elastic projection,
wherein said first lower elastic adhesive is substantially directly located
below said second side elastic projection, and
wherein said second lower elastic adhesive is substantially directly
located below said fourth side elastic projection.
26. A piezoelectric transformer unit, comprising:
a piezoelectric transformer element having a upper element surface, a lower
element surface, and a first side element surface;
a first upper electrode formed on said upper element surface of said
piezoelectric transformer element;
a first lower electrode formed on said lower element surface of said
piezoelectric transformer element;
an insulator casing which houses said piezoelectric transformer element;
a first lead terminal which protrudes from an inner surface of said
insulator casing, supports said piezoelectric transformer element within
said insulator casing, and vertically presses an oscillation nodal point
of said piezoelectric transformer element; and
an insulator elastic member arranged between an oscillation nodal point on
one of said upper, lower, and first side element surfaces of said
piezoelectric transformer element and said insulator casing,
wherein said insulator elastic member corresponds to a first elastic
adhesive applied to said upper casing surface of said insulator casing and
wherein said piezoelectric transformer unit, further comprises:
a second elastic adhesive applied to said lower casing surface of said
casing;
a first side elastic projection projecting from a first side element
surface of said piezoelectric transformer element;
a second side elastic projection projecting from a second side element
surface of said piezoelectric transformer element
a third side elastic projection projecting from a third side element
surface of said piezoelectric transformer element; and
a fourth side elastic projection projecting from a fourth side element
surface of said piezoelectric transformer element.
27. A piezoelectric transformer unit, comprising:
a piezoelectric transformer element having a upper element surface, a lower
element surface, and a first side element surface;
a first upper electrode formed on said upper element surface of said
piezoelectric transformer element;
a first lower electrode formed on said lower element surface of said
piezoelectric transformer element;
an insulator casing which houses said piezoelectric transformer element;
a first lead terminal which protrudes from an inner surface of said
insulator casing, supports said piezoelectric transformer element within
said insulator casing, and vertically presses an oscillation nodal point
of said piezoelectric transformer element; and
an insulator elastic member arranged between an oscillation nodal point on
one of said upper, lower, and first side element surfaces of said
piezoelectric transformer element and said insulator casing,
wherein said insulator elastic member is made of a material comprising one
of silicone and urethane and has a hardness of 30 to 80 according to JIS A
5758.
28. A piezoelectric transformer unit, comprising:
a piezoelectric transformer element having a upper element surface, a lower
element surface, and a first side element surface;
a first upper electrode formed on said upper element surface of said
piezoelectric transformer element;
a first lower electrode formed on said lower element surface of said
piezoelectric transformer element;
an insulator casing which houses said piezoelectric transformer element;
a first lead terminal which protrudes from an inner surface of said
insulator casing, supports said piezoelectric transformer element within
said insulator casing, and vertically presses an oscillation nodal point
of said piezoelectric transformer element; and
an insulator elastic member arranged between an oscillation nodal point on
one of said upper, lower, and first side element surfaces of said
piezoelectric transformer element and said insulator casing,
wherein a contact area between said insulator elastic member and said
piezoelectric transformer element is 0.5 to 1.5 mm.sup.2.
29. A piezoelectric transformer unit as claimed in claim 5, wherein each of
said first to sixth elastic adhesives is made of a material comprising one
of silicone and urethane and has a hardness of 30 to 80 according to JIS K
6253.
30. A piezoelectric transformer unit as claimed in claim 5, wherein a
contact area between each of said first to sixth elastic adhesives and
said insulator casing is 0.5 to 1.5 mm.sup.2.
31. A piezoelectric transformer unit as claimed in claim 5, wherein a
contact area between each of said first to sixth elastic adhesives and
said piezoelectric transformer element is 0.5 to 1.5 mm.sup.2.
32. A piezoelectric transformer unit as claimed in claim 10, wherein each
of said first to sixth side elastic projections is made of a material
comprising one of silicone and urethane and has a hardness of 30 to 80
according to JIS K 6253.
33. A piezoelectric transformer unit, comprising:
a piezoelectric transformer element having a upper element surface, a lower
element surface, and a first side element surface;
a first upper electrode formed on said upper element surface of said
piezoelectric transformer element;
a first lower electrode formed on said lower element surface of said
piezoelectric transformer element;
an insulator casing which houses said piezoelectric transformer element;
a first lead terminal which protrudes from an inner surface of said
insulator casing, supports said piezoelectric transformer element within
said insulator casing, and vertically presses an oscillation nodal point
of said piezoelectric transformer element;
a first insulator elastic member arranged between an oscillation nodal
point on one of said upper, lower, and first side element surfaces of said
piezoelectric transformer element and said insulator casing, wherein said
first insulator elastic member is substantially disposed at a mid point of
a dimension of said first upper electrode, wherein said dimension of said
first upper electrode is parallel to said one of said upper, lower, and
first side element surfaces of said piezoelectric transformer element; and
a second insulator elastic member located next to but not contacting a
nodal line of said piezoelectric transformer element, wherein said second
insulator elastic member does not substantially suppress piezoelectric
oscillation of said piezoelectric transformer element.
34. The piezoelectric transformer unit as claimed in claim 33, further
comprising:
a third insulator elastic member arranged between an oscillation nodal
point on one of said upper, lower, and first side element surfaces of said
piezoelectric transformer element and said insulator casing.
35. The piezoelectric unit as claimed in claim 34, wherein said third
insulator elastic member is substantially disposed at a mid point of a
dimension of said first lower electrode, wherein said dimension of said
first lower electrode is parallel to said one of said upper, lower, and
first side element surfaces of said piezoelectric transformer element.
36. A piezoelectric transformer unit, comprising:
a piezoelectric transformer element having a upper element surface, a lower
element surface, and a first side element surface;
a first upper electrode formed on said upper element surface of said
piezoelectric transformer element;
a first lower electrode formed on said lower element surface of said
piezoelectric transformer element;
an insulator casing which houses said piezoelectric transformer element;
a first lead terminal which protrudes from an inner surface of said
insulator casing, supports said piezoelectric transformer element within
said insulator casing, and vertically presses an oscillation nodal point
of said piezoelectric transformer element; and
first and second insulator elastic members respectively located at first
and second oscillation nodal points of said piezoelectric transformer
element,
wherein said first insulator elastic member is disposed next to an upper
casing surface and a first side casing surface of said insulator casing
and is disposed next to said upper element surface and said first side
element surface of said piezoelectric transformer element, and
wherein said second insulator elastic member is disposed next to said upper
casing surface and said first side casing surface and is disposed next to
said upper element surface and said first side element surface.
37. A piezoelectric transformer unit, comprising:
a piezoelectric transformer element having a upper element surface, a lower
element surface, and a first side element surface;
a first upper electrode formed on said upper element surface of said
piezoelectric transformer element;
a first lower electrode formed on said lower element surface of said
piezoelectric transformer element;
an insulator casing which houses said piezoelectric transformer element;
a first lead terminal which protrudes from an inner surface of said
insulator casing, supports said piezoelectric transformer element within
said insulator casing, and vertically presses an oscillation nodal point
of said piezoelectric transformer element;
a first insulator elastic member located at a first oscillation nodal point
of said piezoelectric transformer element,
wherein said first insulator elastic member projects from said first side
element surface of said piezoelectric transformer element; and
a second insulator elastic member located next to but not contacting a
nodal line of said piezoelectric transformer element, wherein said second
insulator elastic member does not substantially suppress piezoelectric
oscillation of said piezoelectric transformer element.
38. The piezoelectric transformer unit as claimed in claim 37, further
comprising:
a third insulator elastic member located at a second oscillation nodal
point of said piezoelectric transformer element,
wherein said third insulator elastic member projects from a second side
element surface of said piezoelectric transformer element.
39. The piezoelectric transformer unit as claimed in claim 8, wherein said
first side element surface opposes said second side element surface and
wherein said third side element surface opposes said fourth side element
surface,
wherein said first side elastic projection is substantially disposed at a
first mid point of a first dimension of said first upper electrode,
wherein said first dimension of said first upper electrode is parallel to
said first side element surface, and
wherein said second side elastic projection is substantially disposed at a
second mid point of a second dimension of said first upper electrode,
wherein said second dimension of said first upper electrode is parallel to
said second side element surface.
40. The piezoelectric transformer unit as claimed in claim 8, further
comprising:
a first upper elastic projection projecting from said upper surface of said
piezoelectric transformer element and disposed next to an upper casing
surface of said insulator; and
a first lower elastic projection projecting from said lower surface of said
piezoelectric transformer element and disposed next to a lower casing
surface of said insulator.
41. The piezoelectric transformer unit as claimed in claim 6, wherein said
first elastic projection is a first side elastic projection and is
disposed next to a first side casing surface of said insulator casing and
projects from said first side element surface of said piezoelectric
transformer element.
42. The piezoelectric transformer unit as claimed in claim 34, further
comprising:
a second upper electrode formed on said upper element surface of said
piezoelectric transformer element,
wherein said second insulator elastic member is substantially disposed at a
mid point of a dimension of said second upper electrode, wherein said
dimension of said second upper electrode is parallel to said one of said
upper, lower, and first side element surfaces of said piezoelectric
transformer element.
Description
FIELD OF THE INVENTION
The present invention generally relates to a piezoelectric transformer unit
which is used in many types of devices. For example, piezoelectric
transformer units are used in inverter circuits for cold-cathode tube
backlighting liquid crystal display panels in notebook personal computers
and car navigation systems, in adapter power supply circuits generally
used in consumer electronics, and in high-voltage generator circuits such
as electronic copying machines. More particularly, the present invention
relates to the manner in which a piezoelectric transformer element is held
within a piezoelectric transformer casing.
BACKGROUND OF THE INVENTION
FIG. 12(a) shows a vertical cross sectional view of a conventional
piezoelectric transformer unit, and FIG. 12(b) shows a horizontal cross
sectional view of the unit. As shown in the figure, the transformer unit
comprises a piezoelectric transformer element 11, an upper case 12a, a
lower case 12b, upper lead terminals 13a, lower lead terminals 13b, and
projections 14.
The upper and lower cases 12a and 12b are made of molded resin, and the
lead terminals 13a and 13b are insert-molded into the cases 12a and 12b.
Specifically, three upper lead terminals 13a are insert-molded in the
upper case 12a, and three lower lead terminals 13b are insert molded in
the lower case 12b.
As shown in FIG. 12(b), the piezoelectric transformer element 11 has three
electrodes 11a formed on its lower surface. Also, although not shown in
the figure, the element 11 has three similarly disposed electrodes 11a
formed on its upper surface. The lower lead terminals 13b respectively
contact oscillation nodal points on the electrodes 11a on the lower
surface of the element 11, and the upper lead terminals 13a respectively
contact oscillation nodal points on the electrodes 11a on the upper
surface of the element 11. Thus, the lead terminals 13a and 13b support
the piezoelectric transformer element 11 within the casing 12a and 12b as
shown in FIG. 12(a).
Also, the projections 14 are formed at various locations on the inner
surfaces of the casing 12a and 12b and protrude towards the interior of
the casing 12a and 12b. The purpose of the projections 14 is to prevent
the piezoelectric transformer element 11 from excessively shifting from a
predetermined position with respect to the lead terminals 13a and 13b.
In the conventional device described above, the piezoelectric transformer
element 11 is only supported by the elasticity of the lead terminals 13a
and 13b at the upper and lower surfaces of the element 11. As a result,
any jolt or impact to the device may easily cause the piezoelectric
transformer element 11 to shift horizontally with respect to the lead
terminals 13a and 13b and abut against the projections 14 and/or inner
wall of the casing 12a and 12b. When the element 11 touches the projection
14 or casing 12a and 12b, the oscillation characteristics of the element
11 are deteriorated. In addition, when the element 11 abuts against the
projections 14 or casing 12a and 12b, an oscillation having a frequency in
the audible range is added to the piezoelectric transformer element 11,
and such oscillation is propagated to the casing 12a and 12b and causes
noise.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a piezoelectric
transformer unit that does not shift in position if an impact is applied
to the unit and has a high quality output.
In order to achieve the above and other objects, a piezoelectric
transformer unit is provided. The unit comprises: a piezoelectric
transformer element having a upper element surface, a lower element
surface, and a first side element surface; a first upper electrode formed
on said upper element surface of said piezoelectric transformer element; a
first lower electrode formed on said lower element surface of said
piezoelectric transformer element; an insulator casing which houses said
piezoelectric transformer element; a first lead terminal which protrudes
from an inner surface of said insulator casing, supports said
piezoelectric transformer element within said insulator casing, and
vertically presses said an oscillation nodal point of said piezoelectric
transformer element; and an insulator elastic member arranged between an
oscillation nodal point on one of said upper, lower, and first side
element surfaces of said piezoelectric transformer element and said
insulator casing. Also, said insulator elastic member is arranged on or
near a nodal line of the piezoelectric transformer element. The nodal line
is perpendicular to the one of the upper, lower and first side element
surface of the piezoelectric transformer element.
In the conventional example discussed above, the piezoelectric transformer
element is supported via the lead terminals at the oscillation nodal
points of the transformer element. However, experiments conducted by the
inventors indicated that, if the oscillating body is additionally
supported at a nodal point by an elastic body, the energy conversion
efficiency of the body is not significantly reduced. In other words, by
appropriately selecting the contact area between the elastic body and the
piezoelectric transformer element, the hardness of the elastic body, and
the position of the nodal point, the energy conversion efficiency is not
substantially reduced.
In the present invention, the piezoelectric transformer element is
supported at its nodal points by lead terminals and by an elastic body.
Preferably, the position of the transformer element which contacts the
elastic body is a position at which a nodal line of the transformer
element exists. In the present invention, the elastic body has hardness of
30 to 80 (according to JIS K 6253). If the hardness is less than the above
range, holding the transformer element at a predetermined position is
difficult. Also, if the hardness is greater than the above range, the
energy conversion efficiency is substantially reduced. For the same
reasons, the contact area between the elastic body and the transformer
element is set to equal 0.5 to 1.5 mm.sup.2 per position when the area of
the piezoelectric transformer element is 200 to 300 mm.sup.2, the
thickness of the element is 0.5 to 1.5 mm, and the number of positions
where the elastic body contacts the element is 10 to 12).
Holding the piezoelectric transformer element by the elastic body at the
nodal points on the sides of the piezoelectric transformer element
prevents the element from being horizontally shifted by the oscillation of
the element itself or by an external force. Holding the piezoelectric
transformer element by the elastic body at the nodal points on the upper
and lower surfaces of the piezoelectric transformer element prevents the
element from being tilted by the oscillation of the element itself or by
an external force. Therefore, the novel constitution described above
prevents the contact point between the piezoelectric transformer element
and the lead terminal from being shifted from the nodal point. Thus, the
lead terminal does not hinder the oscillation of the piezoelectric
transformer element, and the energy conversion efficiency of the element
is maintained. Also, the novel constitution prevents the piezoelectric
transformer element from contacting the casing and generating noise.
BRIEF DESCRIPTION OF THE DRAWINGS
The above objects and advantages of the present invention will become more
apparent by describing in detail preferred embodiments thereof with
reference to the attached drawings in which:
FIG. 1 is an exploded perspective view illustrating a first embodiment of
the present invention;
FIG. 2 is a top view illustrating the first embodiment of the present
invention;
FIG. 3 is an enlarged view illustrating a method for securing a
piezoelectric transformer element to a casing in the first embodiment of
the present invention;
FIG. 4(a) shows a top view illustrating an upper lead terminal used in the
various examples of the present invention;
FIG. 4(b) shows a side view illustrating the upper lead terminal used in
the various examples of the present invention;
FIG. 5(a) shows a top view illustrating a lower lead terminal used in the
various examples of the present invention;
FIG. 5(b) shows a side view illustrating the lower lead terminal used in
the various examples of the present invention;
FIG. 6 is an exploded perspective view illustrating a second embodiment of
the present invention;
FIG. 7 is an exploded perspective view illustrating a third embodiment of
the present invention;
FIG. 8 is a top view illustrating the third embodiment of the present
invention;
FIG. 9 is a cross sectional view taken along line A-A' of FIG. 8;
FIG. 10 is a cross sectional view taken along line B-B' of FIG. 8;
FIG. 11(a) shows a top view illustrating a piezoelectric transformer
element of a third example of the present invention;
FIG. 11(b) shows a side view illustrating the piezoelectric transformer
element of the third example;
FIG. 11(c) shows a cross sectional view taken along line A-A' of FIG.
11(a);
FIG. 12(a) shows a vertical cross sectional view of a conventional
piezoelectric transformer unit; and
FIG. 12(b) shows a horizontal cross sectional view of the conventional
piezoelectric transformer unit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following description of the preferred embodiments discloses specific
configurations, components, and values. However, the preferred embodiments
are merely examples of the present invention, and thus, the specific
features described below are merely used to more easily describe such
embodiments and to provide an overall understanding of the present
invention. Accordingly, one skilled in the art will readily recognize that
the present invention is not limited to the specific embodiments described
below. Furthermore, the descriptions of various configurations,
components, and values of the present invention which would have been
known to one skilled in the art are omitted for the sake of clarity and
brevity.
First embodiment
FIG. 1 is an exploded perspective view illustrating a piezoelectric
transformer unit in accordance with a first embodiment of the present
invention. FIG. 2 is a top view illustrating a positional relationship
between components of the unit.
As shown in the figures, the piezoelectric transformer unit comprises a
piezoelectric transformer element 1, a casing 2 having an upper case 2a
and a lower case 2b, upper lead terminals 3a, lower lead terminals 3b,
elastic adhesive 4, and snap fit fingers 5.
The upper lead terminals 3a are insert-molded in the upper case 2a, and the
lower lead terminals 3b are insert-molded in the lower case 2b. The snap
fit fingers 5 protrude from the upper case 2a and mate with finger
recesses 5a in the lower case 2b in a snap fit fashion to secure the cases
2a and 2b together.
When the transformer element 1 vibrates, nodal regions within the element 1
exist at which the amplitude of the vibrations is a minimum. In the
example shown in FIG. 1, some of the nodal regions correspond to the
vertical cross sectional area of the element 1 at approximately the
mid-points of the upper electrodes 1a taken along the longer side of the
element 1. For instance, with respect to the left portion of the element
1, a first nodal region intersects the leftmost upper electrode 1a at an
upper nodal line UN1 which is perpendicular to both of the longer side
walls of the element 1 and which roughly bisects the leftmost upper
electrode 1a. Also, the first nodal region intersects the leftmost lower
electrode (not shown) at a lower nodal line (not shown) which is
perpendicular to both of the longer side walls of the element 1 and which
roughly bisects the rightmost lower electrode (not shown). Finally, the
nodal region intersects the longer side walls of the element 1 at side
nodal lines SN1, each of which connect the upper nodal line UN1 and the
lower nodal line (not shown). FIG. 1 also illustrates second and third
nodal regions which respectively form second and third nodal lines UN2 and
SN2 and UN3 and SN3 at the cross sectional mid-points of the middle and
rightmost upper electrodes 1a. In addition, one of ordinary skill in the
art can easily determine where the nodal regions of the element 1 exist.
Pieces of elastic adhesive 4 are applied to the upper case 3a at two
locations and are applied to the lower case 3b at three locations. In
particular, each piece of elastic adhesive 4 is located along the side
wall of the case 2a (or 2b) at a point which coincides with a nodal line
of the transformer element 1.
The element 1 is housed within the casing 2 by sandwiching the element 1
between the upper and lower cases 2a and 2b and snap fitting the fingers 5
into the finger recesses 5a. When the element 1 is housed in the casing 2,
it is attached to the upper case 2a and the lower case 2b via the elastic
adhesive 4. As a result, the element 1 is adhesively and elastically
secured to the casing 2 without directly contacting the inner walls of the
cases 2a and 2b.
FIG. 3 is an enlarged diagram showing an illustrative example of the manner
in which the piezoelectric transformer element 1 is secured within the
casing 2. First, the elastic adhesive 4 is applied to the lower case 2b at
the various locations described above. Then, the piezoelectric transformer
element 1 is lowered into the lower case 2b, and the adhesive 4 surrounds
the corner edges of the element 1 to securely and elastically fasten the
element to lower case 2b. In particular, the adhesive 4 contacts nodal
lines of the element 1, and the points at which the adhesive 4 contacts
the nodal lines can be considered nodal points. Also, due to the existence
of the adhesive 4, a certain distance exists between the piezoelectric
transformer element 1 and the inner walls of the lower case 2b.
Afterwards, the elastic adhesive 4 is applied to the inner walls of the
upper case 2a at the locations described above, and the upper case 2a is
lowered towards the element 1 and mounted to the lower case 2b. As in the
situation of the lower case 2b, the adhesive 4 contained in the upper case
2a surrounds the corner edges of the element 1 to securely and elastically
fasten the element 1 to upper case 2a. Furthermore, the adhesive 4
contacts the element 1 at various nodal points.
As described above, the piezoelectric transformer element 1 is elastically
held in the casing 2 via the adhesive 4 and does not directly touch the
casing 2. As a result, the oscillation of the piezoelectric transformer
element 1 is not obstructed, and no noise is created, even if the unit is
jolted.
First example
In order to illustrate the advantages of the first embodiment, a first
example of such embodiment will be specifically described. In the example,
the piezoelectric transformer element 1 has a length L.sub.P which equals
42 mm, a width W.sub.P which equals 5.5 mm, and a thickness t.sub.p which
equals 1 mm. Also, when the upper and lower cases 2a and 2b are secured
together, the casing 2 has a length L.sub.C equal to 44.4 mm, a width
W.sub.C equal to 7.8 mm, and thickness t.sub.c equal to 3.2 mm. Also, the
material from which the casing 2 is molded is a liquid crystal polymer
that is made by Dupont and is known as Zenite 7130.
FIGS. 4(a) and 4(b) are respective top and side views of the upper lead
terminal 3a. The length a.sub.UL from the inner surface of the side wall
of the upper case 2a to the tip of the lead terminal 3a equals 3.1 mm, and
the width of the tip b.sub.UL equals 0.4 mm. Also, the width c.sub.UL of
the portion of the upper lead terminal 3a which is adjacent to the upper
case 2a equals 1.0 mm and is wider than the width b.sub.UL of the tip to
provide the terminal 3a with strength as a spring material. Also, the lead
terminal 3a is made of a phosphor bronze having a thickness d.sub.UL which
equals 0.1 mm and is nickel-plated to a thickness of 2 to 5 .mu.m.
Furthermore, as shown in FIG. 4(b), the tip of the upper lead terminal 3a
has a "V" shaped step having a height e.sub.UL which equals 0.45 mm. The
dimension of the height e.sub.UL includes the dimension of the thickness
d.sub.UL of the terminal 3a.
The upper lead terminal 3a contacts the piezoelectric transformer element 1
with the bottom edge of the "V" shaped step and thus, contacts the element
along a line having a length equal to the length b.sub.UL of the step
(i.e. 0.4 mm). With respect to the spring-like properties of the upper
lead terminal 3a, it contacts the piezoelectric transformer element 1 with
a vertical push stroke of about 0.5 mm and a pressure force of 50 to 60
gf.
FIGS. 5(a) and 5(b) are respective top and side views of the lower lead
terminal 3b. The length f.sub.LL from the inner surface of the side wall
of the lower case 2b to the tip of the lead terminal 3b equals 3.1 mm, and
the width of the tip g.sub.LL equals 0.4 mm. Also, the width h.sub.LL of
the portion of the lower lead terminal 3b which is adjacent to the lower
case 2b equals 1.0 mm and is wider than the width g.sub.LL of the tip to
provide the terminal 3b with strength as a spring material. As in the case
of the upper lead terminal 3a, the lower lead terminal 3b is made of a
phosphor bronze having a thickness i.sub.LL which equals 0.1 mm and is
nickel-plated to a thickness of 2 to 5 .mu.m. Moreover, as shown in FIG.
5(b), the tip of the lower lead terminal 3b has a "Z" shaped step having a
height j.sub.LL which equals 0.6 mm. The dimension of the height j.sub.LL
includes the dimension of the thickness i.sub.LL of the terminal 3b.
The lower lead terminal 3b contacts the piezoelectric transformer element 1
with the upper surface of the "Z" shaped step which has an area equal to
0.25 mm.sup.2. The spring-like properties of the lower lead terminal 3b
are the same as the properties of the upper lead terminal 3a. Namely, the
terminal 3b contacts the piezoelectric transformer element 1 with a
vertical push stroke of about 0.5 mm and a pressure force of 50 to 60 gf.
With respect to the elastic adhesive 4, a silicone related adhesive having
excellent elasticity and adhesion and having a hardness of 30 to 80 after
molding (according to JIS K 6253) is used. An example of such an adhesive
is a product called White Sealer which is manufactured by HOLTS. In the
present example, a piece of elastic adhesive 4 having a volume from 0.25
ml to 0.75 ml is deposited at each location on the inner surface of the
upper and lower case 2a and 2b. Also, the contact area between the
piezoelectric transformer element 1 and each piece of the elastic adhesive
4 is adjusted to equal from 0.5 mm.sup.2 to 1.5 mm.sup.2 after the element
1 is placed in contact with the adhesive 4.
After a piezoelectric transformer unit having the above dimensions and
properties was created, various tests were conducted to determine the
quality and reliability of the unit. Specifically, a noise level
evaluation, an electrical characteristic evaluation, a vibration test, an
impact test, and a reliability test were performed, and the following
results were obtained.
With respect to the noise level evaluation, the noise levels of the
piezoelectric transformer units corresponding to the present example and
the noise levels of conventional units (e.g. the unit illustrated in FIG.
12) were measured. The noise levels of the units of the present example
were all background noise level, but some of the conventional units had
noise levels which were several dB to 10 dB higher than the background
noise level. Specifically, about 30% of the conventional units had the
higher noise levels.
With respect to the electrical characteristic evaluation, the energy
conversion efficiency of the piezoelectric units of the present embodiment
was 95% or higher. Such result is just as good as the efficiency of the
conventional units in which the piezoelectric transformer element is held
only by the lead terminals.
The vibration test was conducted on 20 units that were manufactured in
accordance with the present example. During the test, vibrations of 3 G
and cycles of 15 Hz to 1 kHz were applied to each transformer unit in the
X, Y, and Z directions of the piezoelectric transformer element 1.
Specifically, the vibrations were applied for 120 cycles in the X
direction, 120 cycles in the Y direction, and 120 cycles in the Z
direction. Since each cycle has a duration of one minute, the vibrations
were applied to each side of each unit for two hours. After the vibration
test, the noise level and the electrical characteristics of each of the
units were the same as the noise levels and electrical characteristics
before the vibration test. Therefore, the piezoelectric units were
virtually unaffected by the vibrations.
The impact test was also conducted on 20 piezoelectric transformer units
that were manufactured in accordance with the present example. During the
test, an impact of 100 G lasting 10 msec was repeatedly applied in the -X,
+X, -Y, +Y, -Z, and Z directions of the piezoelectric transformer element
1. Specifically, the impact was applied to each unit 10 times in each
direction (i.e. a total of 60 times). As in the vibration test, no change
occurred in the noise level and the electrical characteristics of the
units before and after the impact test. Thus, the piezoelectric
transformer units of the present embodiment have an excellent reliability
against external stress.
The reliability test was conducted on 20 units, and the units were
subjected to high temperatures, low temperatures, and thermal shocks. The
reliability test indicated no increase in the noise level or decrease in
energy conversion efficiency of the piezoelectric transformer units. As a
result, they have an excellent reliability against environmental
variations.
Tests and evaluations similar to the ones described above were also
conducted on piezoelectric transformer units in which the contact area
between the piezoelectric transformer element 1 and each piece of elastic
adhesive 4 was less than 0.5 mm.sup.2. (In such case, the coated volume of
the elastic adhesive 4 is less than 0.25 ml). The electrical
characteristic evaluation of the energy conversion efficiency of the units
was the same as the results of the units manufactured in accordance with
the present example. However, noise occurred at an occurrence ratio of
about 5%. Also, after the vibration and impact tests, noise occurred at an
occurrence ratio of about 15%.
Also, similar evaluations were performed on units in which the contact area
between the piezoelectric transformer element 1 and each piece of elastic
adhesive 4 was larger than 1.5 mm.sup.2. (In such case, the coated volume
of the elastic adhesive was greater than 0.75 ml). With respect to the
noise level evaluation, the vibration test, the impact test, and the
reliability test, the units performed as well as the units manufactured in
accordance with the present example. However, the electrical
characteristic evaluation revealed that the energy conversion efficiency
of the units was lower than 90%.
In order to evaluate the effect of the hardness of the elastic adhesive 4,
units were manufactured with an adhesive 4 having a hardness lower than
30, and such units were too soft to adequately hold the element 1 within
the casing 2. Also, units were manufactured with an adhesive 4 having a
hardness higher than 80, and such units had an energy conversion
efficiency of less than 90%.
The test results discussed above were obtained by testing units having an
adhesive 4 made of a silicone-related material. Furthermore, the same
results occurred when units having an adhesive made of a urethane-related
material were tested.
Second embodiment
FIG. 6 is an exploded perspective view illustrating a second embodiment of
the present invention. The second embodiment differs from the first
embodiment in that the electrode 11a at the center of the piezoelectric
transformer element 1 is continuously formed around the outer surface of
the element 1. Also, the second embodiment is different because it does
not have a lower lead terminal 3b which contacts the electrode 11a in the
center of the piezoelectric transformer element 1. Also, a piece of
elastic adhesive 4 is applied at a position corresponding to the midpoint
of the length of the piezoelectric transformer element 1, whereas the
corresponding piece of adhesive 4 is positioned slightly off the midpoint
position.
Second example
In the second example, the piezoelectric transformer element 1, the casing
2, and the lead terminals 3a and 3b have the same shapes and dimensions as
the shapes and dimensions discussed in conjunction with the first example.
With respect to the elastic adhesive 4, White Sealer was used and was
applied to the upper case 2b at two positions and to the lower case 2b at
three positions. Also, each piece of elastic adhesive 4 having a volume
from 0.25 ml to 0.75 ml was deposited at each location on the inner
surface of the upper and lower cases 2a and 2b. Also, the contact area
between the piezoelectric transformer element 1 and each piece of the
elastic adhesive 4 was adjusted to equal from 0.5 mm.sup.2 to 1.5 mm.sup.2
after the element 1 was placed in contact with the adhesive 4.
The piezoelectric transformer units were also subjected to the noise level
evaluation, the electrical characteristic evaluation, the vibration test,
the impact test, and the reliability test. The results obtained during the
testing of the second example were similar to the results obtained during
the testing of the first example.
As described above, in the first example, the elastic adhesive 4 is
attached to the central lower lead terminal 3b and thus, may adversely
alter the force with which the lead terminal 3b presses against the
piezoelectric transformer element. On the other hand, in the second
example, the central lower lead terminal 3b has been removed to allow the
elastic adhesive to be applied to the center position. Therefore, the
above problem is eliminated, and the manufacturing efficiency of the
piezoelectric transformer unit is increased.
Third embodiment
FIG. 7 is an exploded perspective view illustrating a third embodiment of
the present invention, and FIG. 8 is a top view illustrating a positional
relationship between various components of the third embodiment. Also,
FIG. 9 is a cross sectional view taken along the line A-A' of FIG. 8, and
FIG. 10 is a cross sectional view taken along the line B-B' of FIG. 8.
Also, in FIGS. 7 to 10, components which are the same or similar to the
components described in conjunction with FIGS. 1 to 6 are denoted by the
same reference numerals, and a description of such components is omitted
for the sake of brevity.
In the third embodiment, the elastic adhesive 4 used in the first and
second embodiments is not used. Instead, conical or spheroidal elastic
projections made of rubber material such as silicone rubber or urethane
rubber are arranged and formed at nodal points on the front, rear, and
side surfaces of the piezoelectric transformer element 1 by a screen
printing process or similar process. For example, as shown in FIGS. 7 to
10, upper elastic projections 6a are arranged on the upper surface of the
piezoelectric transformer element 1, lower elastic projections 6b are
arranged on the lower surface, and side elastic projections 6c are
arranged on the side surfaces. Also, when the upper and lower cases 2a and
2b are mounted together and sandwich the element 1, the projections 6a,
6b, and 6c do not need to contact the side walls of the cases 2a and 2b.
The elastic projections are made of a material comprising one of silicone
and urethane and has a hardness of 30 to 80 according to JIS K 6253.
Third example
In the third example, the piezoelectric transformer element 1, the casing
2, and the lead terminals 3a and 3b have the same shapes and dimensions as
the shapes and dimensions discussed in conjunction with the first and
second examples.
FIG. 11 shows a top view, a side view, and a cross sectional view
illustrating the positions of the elastic projections 6a, 6b, and 6c
printed on the piezoelectric transformer element 1. As shown in the
figure, the elastic projections 6a, 6b, and 6c are provided at a total of
12 positions on the element 1. Three upper elastic projections 6a are
formed on the upper surface of the element 1, three lower elastic
projections 6b are formed on the lower surface, four side elastic
projections 6c are formed on the long side surfaces of the element 1, and
two side elastic projections 6c are formed on the short side surfaces.
As shown in FIG. 11, each upper elastic projection 6a has a diameter
k.sub.UEP which equals 1.0 mm and a height m.sub.UEP which equals 0.35 mm.
Each lower elastic projection 6b has a diameter n.sub.LEP which equals 1.0
mm and a height p.sub.LEP which equals 0.25 mm. Each side elastic
projection 6c has a conical shape with an elliptical base. The long axis
of the elliptical base has a length q.sub.SEP which equals 1.0 mm and a
short axis length r.sub.SEP which equals 0.5 mm. Also, each projection 6c
has a height s.sub.SEP which equals 0.1 mm.
By disposing the elastic projections 6a, 6b, and 6c on the element, the
piezoelectric transformer unit generates an extremely small amount of
noise during operation because the projections 6a, 6b, and 6c prevent the
element 1 from directly touching the casing 2. Also, although not shown in
FIG. 9, a gap of 0.03 mm to 0.1 mm is preferably provided between at least
one of the elastic projections 6a, 6b, and 6c and the casing 2. For
example, some of the projections (e.g. the three lower elastic projections
6b and the rightmost elastic projection 6c) may contact the casing 2
without pressure, and some of the projections (e.g. the three upper
elastic projections 6a and the leftmost elastic projection 6c) may be
separated from the casing 2 by a gap of 0.03 mm to 0.1 mm. Therefore, the
oscillation of the piezoelectric transformer element 1 is not hindered,
and the piezoelectric transformer unit has an excellent electrical
characteristic. Furthermore, not only is the element held by the lead
terminals 3a and 3b, but it is also protected by the elastic projections
6a, 6b, and 6c, and thus, the piezoelectric transformer unit has a very
high resistance to external stress.
Also, unlike the first and second examples, the height of the elastic
projections 6a, 6b, and 6c can be adjusted by changing the printing
quantity of the screen printing operation or by changing similar
quantities of similar operations. Thus, the heights of the projections can
be adjusted based on the gap between the piezoelectric transformer element
1 and the casing 2. Therefore, the design of the piezoelectric transformer
element 1 can be easily modified so that it can fit in many differently
sized casings 2.
Piezoelectric transformer units made in accordance with the third example
were also subjected to the noise level evaluation, the electrical
characteristic evaluation, the vibration test, the impact test, and the
reliability test. The results obtained during the testing of the third
example were similar to the results obtained during the testing of the
first and second examples.
Fourth example
In the fourth example, the piezoelectric transformer element 1, the casing
2, and the lead terminals 3a and 3b have the same shapes and dimensions as
the shapes and dimensions discussed in conjunction with the first, second,
and third example.
In the fourth example, the upper and lower elastic projections 6a and 6b
used in the third example are removed, and only the side elastic
projections 6c are formed on the side surfaces of the piezoelectric
transformer element 1. Also, the elastic adhesive 4 is applied to the
upper case 2a and the lower case 2b at the positions described above in
conjunction with the first example, and the piezoelectric transformer
element 1 is adhesively attached at the upper and lower surfaces to the
casing 2. However, in the fourth example, the adhesive 4 is prevented from
spreading around the sides of the piezoelectric transformer element 1. The
dimensions of the side elastic projections 6c are the same as the
projections 6c used in the third example, and six projections 6c are
placed around the side surfaces of the element 1 as described in the third
example.
Piezoelectric transformer units made in accordance with the fourth example
were subjected to the noise level evaluation, the electrical
characteristic evaluation, the vibration test, the impact test, and the
reliability test. The results obtained during the testing of the fourth
example were similar to the results obtained during the testing of the
first, second, and third examples.
In the illustrative embodiments and examples described above, the
piezoelectric transformer unit has a piezoelectric transformer element
which is pressed and held by upper and lower lead terminals at its nodal
points and is held by elastic members which are provided at nodal points
between the element and a casing. As a result, the unit has many
advantages.
For example, the piezoelectric transformer element does not directly
contact the casing because it is protected by the elastic members.
Therefore, if the piezoelectric transformer element generates an
oscillation that has a frequency in audible sound range, the oscillation
does not propagate to the casing, and the amount of noise caused by
operating the piezoelectric transformer unit is dramatically reduced.
Also, the piezoelectric transformer element is held at its nodal points by
an elastic member which is relatively soft and which contacts the element
at a limited contact area. As a result, the oscillation of the
piezoelectric transformer element is not hindered, and the piezoelectric
transformer unit has excellent electrical characteristics.
In addition, if an external vibration or impact is applied to the unit, the
piezoelectric transformer element does not shift with respect to the
casing. Therefore, points at which the lead terminals contact the
piezoelectric transformer element do not shift from the nodal points, and
the conversion efficiency of the piezoelectric transformer unit is
maintained.
Also, if an external vibration or impact is applied to the unit, the
piezoelectric transformer element is protected from abutting against the
casing. Thus, noise which would have been caused by such collision is
avoided.
The previous description of the preferred embodiments is provided to enable
a person skilled in the art to make or use the present invention.
Moreover, various modifications to these embodiments will be readily
apparent to those skilled in the art, and the generic principles defined
herein may be applied to other embodiments without the use of inventive
faculty. Therefore, the present invention is not intended to be limited to
the embodiments described herein but is to be accorded the widest scope as
defined by the claims.
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